This invention relates generally to wavelength division multiplexing and more particularly to an integrated waveguide grating optical device, based on echelle grating technology, capable of interleaving and de-interleaving different wavelength channels.
Driven by the growth of the Internet, consumer demand for data transmission bandwidth has quickly surpassed that of voice. To satisfy this demand, optical networks have been deployed all over the world. The amount of information that can be transmitted on a single fibre optic cable is typically boosted by multiplexing multiple wavelengths on a single optical fibre, allowing it to carry as much data as multiple fibres, each propagating an optical signal at a specific wavelength. This process is referred to as Wavelength Division Multiplexing (WDM), or, in cases when 16 or more wavelength channels are combined, as Dense Wavelength Division Multiplexing (DWDM). This technique allows many different wavelengths of light propagate simultaneously along an optical fibre. Since the combined wavelengths support predetermined channel spacing, the resulting multiplexed signal is also referred to as a channelized signal.
At present, a variety of technologies have been developed that support DWDM data transmission, including: thin film filters, fibre Bragg gratings, integrated waveguide demultiplexers based on phased Arrayed Waveguide Gratings (AWG), and Echelle Gratings (EG). The latter two techniques are optionally used in grating-on-a-chip spectrometers. Integrated devices have many advantages over conventional optical components such as compactness, reliability, reduced fabrication and packaging costs, high-volume manufacturability, and potential monolithic integration with a variety of active devices.
AWGs are often employed for multiplexing/de-multiplexing tasks. An optical waveguide device to achieve this task is for example described in U.S. Pat. No. 5,002,350 to Dragone, issued Mar. 26, 1991, and these techniques are constantly extended and improved, as for example illustrated in U.S. Pat. No. 6,272,270 to Okayama, issued Aug. 7, 2001.
One parameter used in describing the channel response of AWG and EG techniques is the spectral finesse. The fine spectral finesse, which is beneficial for large channel count devices, is often difficult to achieve, and consequently, conventional optical components that have high spectral finesse tend to be quite costly. A solution to this problem is found in the common practice of de-interleaving the multiplexed optical signal. De-interleaving a wavelength multiplexed optical signal converts the multiplexed single signal into two or more signals, each containing optical signals corresponding to certain predetermined wavelength channels. Typically the optical signals provided by the interleaver correspond to a set of signals having non-adjacent wavelength channels at the input port of the interleaver. For example, given an original wavelength multiplexed optical signal with eight predetermined wavelength channels provided to an interleaver, after de-interleaving channels 0, 2, 4, and 6 are provided to a first output port, whereas channels 1, 3, 5, and 7 are provided to a second output port. As a result, the width of the single wavelength channels is effectively doubled, and the DWDM component demands less stringent requirements on passband width and on slopes of passband edges.
Since the design of a de-interleaver depends on the application wavelength window in which the de-interleaver is sought to operate, a few considerations regarding the wavelength range are in order. Optical amplifiers used in the transmission of WDM or DWDM optical signals are typically chosen to ensure that they support the appropriate wavelength range. Currently the most commonly used amplifiers are Erbium-Doped Fibre Amplifiers (EDFA). The wavelength windows range from 1530 nm to 1565 nm (C-band), and from 1570 nm to 1610 nm (L-band). Each of the wavelength windows can accommodate about 40 channels with 100 GHz (xcx9c0.8 nm) spacing, or 80 channels with 50 GHz (xcx9c0.4 nm) spacing. A de-interleaver for use in reducing spectral finesse requirements of DWDM components operates within these same bands.
Further, the described optical device performing the task of de-interleaving is bi-directional. This means that this device not only de-interleaves optical signals, but also for interleaves two or more optical signals into one single signal. Therefore, the optical device will be referred to as an interleaver/de-interleaver, and when talking about an interleaver or de-interleaver only, the bi-directionality of the device is implied. The bi-directionality also implies that input ports for interleaving functionality become output ports for de-interleaving functionality, and so forth.
As is well known in the art, a Fabry-Perot etalon is a common optical component used to fulfill the basic functionality of a de-interleaving device. A description of such an etalon can be found in standard textbooks on the subject matter (G. R. Fowles, Introduction to Modern Optics, 2nd ed., Dover Publications, Inc, New York, 1989). A method of using a Fabry-Perot etalon as a means of separating out odd and even wavelengths from an incoming multiplexed signal is for example illustrated in U.S. Pat. No. 6,208,444 to Wong et al., issued Mar. 27, 2001. However, the major problem associated with a single cavity Fabry-Perot etalon, as well as other types of interference filters, is the narrowness of the peaks. This imposes unacceptably severe tolerances on the optical sources that provide the individual optical signals at specific wavelengths because the peak intensity of the wavelength spectrum provided by the source must accurately correspond to the predetermined wavelength channels in order to avoid attenuation of the optical signal by the etalon.
It would be advantageous to have an optical component that acts as an interleaver/de-interleaver, which does not depend upon conventional, expensive and hard to manufacture techniques of production associated with currently available interleavers. Additionally, it would be advantageous if the optical component is very small, resulting in small package footprint and reduced power consumption. It would be advantageous to provide such a device without requiring the level of channel peak accuracy currently necessary for etalon devices.
It is an object of the invention to provide an integrated interleaver component using echelle grating technology.
The present invention discloses an optical device comprising: an input port for receiving a multiplexed optical signal, including optical signals wherein each pair of wavelength channels out of a plurality of wavelength channels has a predetermined channel spacing; N output ports, with N greater than 1; and an echelle grating for separating the multiplexed optical signal received at the input port in dependence upon a wavelength, and for providing a plurality of channelized signals to each of the output ports; wherein optical signals corresponding to each of a plurality of optical channels xcex1xc2x7N+1:a∈ {0.M} are provided to a same first output port, and optical signals corresponding to each of a plurality of optical channels xcex1xc2x7N+2:a∈ {0.M} are provided to a same second output port, M being a natural number, Mxe2x89xa71.
The invention also describes an optical device comprising: an input port for receiving a multiplexed optical signal, including optical signals within a same industry standard communication band wherein each pair of wavelength channels within the industry standard communication band has a predetermined channel spacing; a first output port; a second output port; and an echelle grating for separating the multiplexed optical signal received at the input port in dependence upon a wavelength, and for providing a plurality of channelized signals to each of the output ports; wherein optical signals corresponding to at least two of the optical channels within the industry standard communication band are provided to the first output port, and at least two other of the optical channels within the industry standard communication band are provided to the second output port.
The present invention further discloses a method of de-interleaving a wavelength multiplexed optical signal comprising the steps of: receiving a wavelength multiplexed optical signal at an input port, said wavelength multiplexed optical signal including optical signals wherein each pair of wavelength channels out of a plurality of wavelength channels has a predetermined channel spacing; separating the wavelength multiplexed optical signal received at the input port in dependence upon wavelength with an echelle grating; and providing a plurality of channelized signals to each of a plurality of N output ports, such that optical signals corresponding to each of a plurality of optical channels xcex1xc2x7N+1:a∈ {0.M} are provided to a same first output port, and optical signals corresponding to each of a plurality of optical channels xcex1xc2x7N+2:a∈ {0.M} are provided to a same second output port, M being a natural number, Mxe2x89xa71.
Additionally, the invention provides a method of de-interleaving a wavelength multiplexed optical signal comprising the steps of: receiving the wavelength multiplexed optical signal at an input port; using an echelle grating separating the wavelength multiplexed optical signal received at the input port in dependence upon wavelength; and, providing a plurality of channelized signals to each of a plurality of output ports such that optical signals corresponding to at least two of the optical channels within an industry standard communication band are provided to the first output port, and at least two other of the optical channels within an industry standard communication band are provided to the second output port.